The present invention relates generally to the field of vehicle diagnostic systems. More specifically, the invention relates to a method and system of associating parts of a vehicle area network message together to simplify the use of vehicle diagnostic equipment.
Virtually all vehicles made today utilize components or systems that are computer controlled, ranging from the engine and transmission to the interior climate control and entertainment center. Additionally, these vehicle components or systems are often capable of exchanging data concerning their operating state across a vehicle area network (VAN) to other related systems.
With the ability to communicate data across a network, these components or systems have become easier to monitor for both performance and operating flaws. This is often accomplished by means of electronic diagnostic tools that interface with one of the vehicle data networks and retrieve information from the various components residing on that network. For example, trucks often incorporate an independent data bus for linking many of the truck""s systems and components together, thereby allowing for easy and frequent monitoring of various conditions existing throughout the different systems of the truck.
In order to maintain a certain level of uniformity between the data networks of all the trucks on the road today and in the future, various organizations related to the field set forth protocols that govern not only the physical characteristics of vehicle networks, but also the format of the data that is passed along the networks. One such example, provided solely for illustrative purposes, is protocol J1708/1587 established by the Society of Automotive Engineers (SAE). Protocol J1708/1587 establishes a serial data communications link for exchanging and monitoring data being communicated between microprocessors used in heavy-duty vehicle applications. Protocol J1708 generally defines the hardware requirements of the data communications link, while protocol J1587 deals with the actual data, the format of the data and/or functions that are to be transmitted across the data link.
The communication links in trucks and other vehicles provides for the sharing of data among various components or modules that make up the vehicle. These components or modules can range from functional devices or systems incorporated into the vehicle, to extrinsic devices such as diagnostic equipment. According to one protocol, data sent along the link is grouped into packets known as xe2x80x9cmessagesxe2x80x9d. According to this protocol, each message consists of three parts, with certain portions acting as an addressing or routing service that ensures that the message gets to the appropriate destination on the data link. The three parts of any message transmitted on the data link include 1) a Message Id 2) One or more Parameters and 3) Checksum.
Referring to FIG. 1, which depicts the parts of a typical data message according to an existing protocol. The first part is the Message Identification (MID) 5, which identifies the actual component or control system of the vehicle from which the data was transmitted, such as, for example, the engine, transmission, etc. No two components that are capable of transmitting data may have the same MID.
The second component of a message is a set of data characters, otherwise known as a parameter 7, which makes up the bulk of the message. The first portion of every parameter is reserved for what is known as the Parameter Identification (PID). This reserved portion is used to identify the data being sent by a MID, typically by identifying the particular subsystem or section of the control system that generated the message.
Sometimes messages do not contain PIDs, but instead possess what is known as Subsystem Identification Numbers (SIDs). Occasionally sections of a control system cannot be properly identified by one of the standardized PIDs established by the pre-defined protocol. As such, unique SIDs can be assigned by the organization or agency that established the previously defined protocol. These SIDs can be used to identify those sections of a control system that do not have a pre-defined PID. SIDs should only be assigned to field-repairable or replaceable subsystems for which failures can be detected and isolated by the control system.
After the PIDs or SIDs, the remaining data characters making up the parameter convey the meaning of the message. Included within these remaining data characters is a Failure Mode Identifier (FMI). The FMI is a specific code that describes the type of failure, if any, detected in the subsystem identified by the PID. The FMI, when combined with either the PID or SID, form a diagnostic trouble code (DTC).
The last component of the message is a checksum 9, which is a specific character generated based on the sum of the MID value and the data characters of the message. The checksum is used to verify the error-free transmission of a message across the network.
Currently, most SIDs are defined in relation to certain MIDs. Accordingly, a MID and a SID can be interpreted as a whole, thus properly identifying a component or subsystem of a control system. In contrast, the more commonly utilized PIDs are not defined in relation to most MIDs. Without some form of established relationship, any MID can be thought to correspond to any PID, even though some PIDs are made specifically for certain MIDs. This is especially problematic considering that each vehicle component on the data link, according to existing protocol, is identified by a specific combination of PID and MID values. Accordingly, in order to address one or more components for certain applications, such as diagnostic testing, the specific PID and MID combination for each component must be known. Yet without an easy way to eliminate certain MID-PID combinations, the finding of a specific component or subsystem identifier can be an insurmountable challenge due to the overwhelming number of combinations that can be readily made between MID and PID data.
It would be desirable to establish a correspondence or relationship between different parts of a message as defined by a protocol. However, the existing art does not suggest such a correspondence or relationship.
The invention is directed to a new method of organizing data that corresponds to a pre-defined protocol for a vehicle data link. The new method includes establishing message identification (MID) categories into which MID codes can be organized. Similarly, parameter identification (PID) functions are also established, which permit the organization of PID codes. Specific codes of either code type can then be associated with either certain MID categories or certain PID functions, and vice versa. This allows a specific vehicle component, which is identified by a combination of MID and PID codes, to be specified without requiring one to know the specific code combination identifying that component.